1. Field of the Invention
The present invention is related to paper products such as paperboard and the like, and more particularly to paperboard having improved resistance to moisture penetration therethrough, and a method of making same.
2. Background of the Invention
The term "paperboard" will be used herein as meant in a generic sense for all forms of paper products such as cardboard, boxboard, etc.
A well recognized problem with paperboard is its propensity to absorb moisture. This is a particularly important drawback in the use of paperboard for article containers.
Various solutions have been proposed which renders the paperboard impervious to moisture. For example, U.S. Pat. No. 3,107,837 teaches the wicking and bleeding problems of paperboard, and provides a solution which uses a coating of impervious material, such as polyvinyledine chloride, on the interior surface of a paperboard carton to form a moisture barrier. U.S. Pat. No. 3,328,189 teaches preventing wicking of wwater through a paperboard container by applying a layer of perfluoroalkylmonocarboxylic acid on the inside of a carton blank to form a moisture barrier. U.S. Pat. No. 4,075,372 teaches applying a flexible precoat of a thermoplastic resin of polyvinyl acetate, ethylene vinyl acetate, ethylene vinyl chloride, and then applying a lacquer over the precoat to form a moisture barrier. U.S. Pat. No. 4,198,267 teaches a process for manufacturing paper pulp by adding a composition to the pulp slurry which includes finely divided hydrophobic lubricating particles such as silica, or wax in a hydrocarbon oil carrier liquid, and a minor quantity of a surfactant to assist in spreading the carrier in the aqueous slurry to enhance the distribution and penetration of the lubricating particles in the slurry. U.S. Pat. No. 4,207,142 teaches the use of various paper sizing agents which can be either mixed within the paper pulp from which paper is later made, or to the surface of the paper after it is made. And, U.S. Pat. No. 4,597,831 teaches a method of sizing a paper sheet to render the paper sheet less absorbent to water by applying a foam of rosin the paper surface.